The Interleukin-6 Receptor (IL-6R) is a critical cytokine receptor that plays a significant role in neuroinflammation, a key pathological feature of neurodegenerative diseases including Alzheimer's Disease (AD) and Parkinson's Disease (PD). [1] IL-6R mediates the cellular response to interleukin-6 (IL-6), a pleiotropic cytokine that participates in both acute phase responses and chronic inflammatory processes. [2] The IL-6R signaling pathway has become an important therapeutic target, with tocilizumab (an IL-6R antagonist) showing promise in clinical trials for various neurological conditions. [3]
Interleukin-6 Receptor (IL-6R) is a transmembrane protein encoded by the IL6R gene on chromosome 1q21.3. [4] It exists in two forms: a membrane-bound receptor (mIL-6R) of approximately 80 kDa and a soluble receptor (sIL-6R) generated by proteolytic cleavage or alternative splicing. [5] The membrane-bound IL-6R is expressed on various cell types including hepatocytes, leukocytes, and certain neuronal populations, while the soluble form can bind IL-6 and trigger signaling in cells that express the signal-transducing subunit gp130 but lack IL-6R itself—a phenomenon known as trans-signaling. [6]
The IL-6R pathway is particularly relevant to neurodegeneration because chronic neuroinflammation is a hallmark of both AD and PD. [7] Elevated levels of IL-6 and sIL-6R have been detected in the cerebrospinal fluid (CSF) and post-mortem brain tissue of patients with AD and PD, suggesting that dysregulated IL-6 signaling contributes to disease progression. [8] Genetic studies have also identified IL6R variants as risk factors for AD, further supporting its pathogenic role. [9]
The IL-6R extracellular domain consists of three distinct regions: [10]
The soluble form (~55 kDa) retains the extracellular domain and can: [11]
IL-6R signaling is essential for hepatic acute phase protein synthesis: [12]
IL-6R plays crucial roles in immune cell differentiation: [13]
In the central nervous system, IL-6R signaling contributes to: [14]
IL-6R signaling contributes to AD pathogenesis through multiple mechanisms: [15]
Soluble IL-6R levels correlate with cognitive decline in AD patients: [16]
IL-6R plays important roles in PD pathogenesis: [17]
IL-6R involvement extends to: [18]
| Drug | Mechanism | Status | Application |
|---|---|---|---|
| Tocilizumab | IL-6R antibody | Approved (RA) | Clinical trials for AD/PD |
| Sarilumab | IL-6R antibody | Approved (RA) | Investigational |
| Satralizumab | IL-6R antibody | Approved (NMOSD) | Investigational |
Clinical trials of IL-6R blockade in neurological disorders: [19]
IL-6R measurements show promise as biomarkers: [8:1]
IL-6 and IL-6R in Alzheimer's disease: Implications for future therapeutics (2023). 2023. ↩︎
Interleukin-6: Review of its role in immune regulation and disease (2022). 2022. ↩︎
Tocilizumab in neurodegenerative diseases: Clinical trials and mechanisms (2023). 2023. ↩︎
Soluble IL-6R: Generation and biological significance (2022). 2022. ↩︎
IL-6 trans-signaling via soluble IL-6R: Importance for neuroinflammation (2021). 2021. ↩︎
Neuroinflammation in Alzheimer's and Parkinson's disease (2023). 2023. ↩︎
CSF IL-6 and sIL-6R as biomarkers in neurodegenerative diseases (2022). 2022. ↩︎ ↩︎
IL6R genetic variants and Alzheimer's disease risk (2021). 2021. ↩︎
Crystal structure of IL-6R and binding mechanisms (2020). 2020. ↩︎
ADAM17-mediated shedding of IL-6R in neuroinflammation (2022). 2022. ↩︎
IL-6R in immune cell differentiation and function (2023). 2023. ↩︎
IL-6R signaling mechanisms in Alzheimer's disease (2023). 2023. ↩︎
Soluble IL-6R as cognitive decline biomarker in AD (2022). 2022. ↩︎
IL-6R and neuroinflammation in multiple sclerosis and ALS (2022). 2022. ↩︎
Clinical trials of IL-6R blockade in neurological disorders (2024). 2024. ↩︎